ABSTRACT
The only way to make a new cell is to duplicate a cell that already exists. This simple fact, first established in the middle of the nineteenth century, carries with it a profound message for the continuity of life. This chapter describes the events of the cell cycle and how they are controlled and coordinated. The most basic function of the cell cycle is to duplicate the vast amount of DNA in the chromosomes and then segregate the copies into two genetically identical daughter cells. Most cells require much more time to grow and double their mass of proteins and organelles than they require to duplicate their chromosomes and divide. Some features of the cell cycle, including the time required to complete certain events, vary greatly from one cell type to another, even in the same organism. The cell-cycle control system operates much like a timer that triggers the events of the cell cycle in a set sequence.
